Automatic pilot



pr l 1960 w. G. WHITE 2,934,690

AUTOMATIC PILOT Filed March 6, 1956 3 Sheets-Sheet l IN VEN TOR.

ATTORNEYS April 26, 1960 w. G. WHITE 2,934,690

AUTOMATIC PILOT Filed March 6, 1956 Y 3 Sheets-Sheet 2 INVENTOR. WILFRIDGQRD N WHITE Fig. 3 k

ATTORNEYS April 26, 1960 Filed March 6, 1956 Fig. 6

W. G. WHITE AUTOMATIC PILOT 5 Sheets-Sheet 3 Sensifive Than relay RI?More m}: B1 B2 INVENTOR.

WILFRID GORD WH\TE lam/ 41 w ATTORNEYS United States Patent AUTOMATICPILOT Wilfrid G. White, Dover, Mass., assignor to Wilfrid 0. White &Sons, Inc., Boston, Mass, a corporation of Massachusetts ApplicationMarch 6, 1956, Serial No. 569,799 I 8 Claims. (Cl. 318-489) The presentinvention relates to automatic pilots, and more particularly to improvedand simplified controls for the automatic steering of vessels upon setcourses.

The principal object of any automatic pilot is to eliminate thenecessity for constant attention required during manual steering and theconsequent physical elfort, thus making it possible for the helmsman toleave the wheel to take bearings, lay off new courses, secure loosegear, handle an emergency, or engage in any other activity. By means ofa course-setting device operating in conjunction with a compass readingdevice, the boat is steered on a given heading without attention untilthe setting is changed.

Further objects of a corollary nature include saving fuel and tim'e andassuring safer landfalls by maintaining close adherence to the course.

Automaticpilots have been the subject of intensive study,"developementrand use over a period of many years, but ordinarily'impro'vements have resulted in an increase in cost and complexity ofapparatus, obviating their rise in sinallerfcraft. Certain problemsarise from the characteristics inherent "in'the "compass, and othersfrom the automatic circuits and mechanism adapted to measure thedeparture from course and to apply a proper angle of rudder tocompensate therefor. These problems include the possibility of the boatfollowing an erroneous heading, particularly after a change in thecourse setting. v

Vacuum tube embodiments have the further disadvantages of requiring awarm-up time, and often of requiring critical adjustments and expensiverepairs. It has long been recognized in navigation that any electricalapparatus likely to be influenced by salt spray, humidity, or otherconditions at sea is likely to be unreliable, and should be used onlywith adequate safeguards and alternative automatic or manual means foruse in case of breakdown. Vacuum tube devices are generally of thistype, and they have the still further disadvantage of requiringconsiderable current from the ship's battery during operation.

It is accordingly a particular object of this invention to provide anautomatic pilot having no vacuum tube components, and hence requiring alow 'current drain and q no warm-up time.

A furtherobject is to provide an automatic pilot of simple andstraightforward design, thereby reducing to a minimumrthe number ofcomponents sensitive to ambient conditions, whereby it becomes feasibleto install the to provide a pilot I adapted for alternative manualsteering by a simple and convenient manipulation of the controls, andthat does not cause, appreciable'dragon the steering mechanism M whendisengaged and secured.

A further object is to provide a pilot characterized by Patented Apr.26, 1960 2 freedom from critical adjustments and the tendency to hunt.

With the foregoing and other objects in view, a feature of the presentinvention resides in the provision of a reversible steering motor whichis powered through contacts, of a pair of relays selectively energizedby a steering circuit of novel form. This circuit includes a pair ofcontrol relays each of the type having two separate windings connectedwith their respective energizing circuits in aiding relationship. l

According to another feature, a coil oneach of the control relays isconnected in series with the corresponding coil on the other relay, andthe current for this series circuit is supplied through a singletransistor having a variable input signal derived by photoelectricmeansfrom the compass. This photoelectric means consists of a pair ofphotosensitive devices juxtaposed to continuous sources of light onopposite sides of a suitably supported compass card having a lightaperture.

A feature of construction of the compass resides in the sphericalconstruction of the fluid-filled chamber, with the compass cardsupported at the center of the chamber and the photosensitive devicesbeing situated adjacent the inner Wall of the chamber in position toreceive light from continuous light sources supported symmetricallythereto adjacent the Wall of the chamber on the opposite side of thecompass card.

By the foregoing means there is provided a magnetic compass withphotosensitive means to derive directional information withoutapplication of friction, and apparatus responsive to such informationrequiringa negligible warm-up time.

A further feature of the invention resides in circuit features thatpermit the attainment of relatively high sensitivity in system response,without giving rise to selfsustaining oscillations or hunting. Thus thesteering motor is powered only when the boat is ofi course, with ofdesign and in a typical instance it might be, for example, 30 fromcenter or thereabouts.

A further feature related to the last-mentioned rudder follow-up controlresides in the provision of electrical means for centering the controls,thereby. permitting the pilot device to beset precisely at the desiredconditions necessary for equal response in both directions of steering.j v

A still further feature resides in the provision of a remote maneuveringdevice for disengaging the automatic pilot and permitting steering fromany part of the boat by means of simple manual or pushbutton controls.

Still other features reside in interlock relay means to preventapplication of opposing voltages to the steering motor; in condensermeans for preventing overrunning of the steering motor after removal ofa steering signal; and in other features of construction, modes ofoperation and relationships of the parts which'will become more evidentfrom the followingjdetaileddescription of a preferred embodiment oftheinvention, and from the appended drawings illustrating the same. I g

In the drawings, Fig. l is an oblique diagrammatic view of therudder-{driving mechanism forming a part of ,v theautomatic pilot;

Fig. 2 is a plan view of the binnacle assembly;

Fig. 3 is a side elevation in section of the binnacle assembly;

Figs. 4 and 5 are sectional elevations taken respectively on lines 44and 5-5 of Fig. 3; and

Fig. 6 is a circuit diagram showing the connections between the binnacleassembly, the mechanism of Fig. l, and the remote maneuvering device.

Referring. to Fig. 1, there is shown a steering wheel 12' and a steeringshaft 14 which are parts of the usual manual steering mechanism coupledwith the rudder of a boat. A sprocket 16 is secured to the shaft 14. Ashaft 18 has a sprocket 20 similarly secured to it, and the sprockets 16and 20 are coupled by a drive chain 22. Thus the shafts 14 and 18 are atall times coupled, whether the device is set for manual or automaticsteering.

A sleeve 24 is slidably received over the shaft 18, and has a worm gear26 and a sun gear 28 secured to it. A worm 30 secured to a shaft 32 isengaged with the gear 26, the shaft 32 being permanently coupled withthe armature of a rudder drive motor M. By reason of the worm and gearcoupling, the sleeve 24 may turn only when the motor M revolves; thatis, the transmission of motion through the coupling is irreversible andmust be applied by the worm30 to the gear 26.

A member 34 is pinned to the shaft 18 by a pin 36, and rotatablysupports a pair of planetary gears 38 by their respective shafts 40. Itwill be apparent that although only two planetary gears are shown, agreater number may be used if desired. These gears are permanentlyengagedwith the sun gear 28 and with an outer gear 42. For automaticoperation, as shown, the gear 42 is restrained from rotating by atoothed stop member 44 pivotally supported in the fixed frame 46 of themechanism on pivots 48. The member 44 has an end wise longitudinal slotin which is received a cam 50 eccentrically mounted on a rotatable shaft5'2. The shaft 52 is rotatable between two limit positions substantially180 degrees apart by a Bowden wire 54 having a conveniently accessiblemaster control knob 56 adjacent the wheel 12. The wire 54 is secured toa bell crank lever 58, which is in turn secured to the shaft 52.

As previously stated, the mechanism is illustrated in the condition forautomatic operation, and the knob 56 is pushed substantially to itsdownward extremity. The stop member 44 is engaged with the gear 42.Under these conditions the wheel 12 cannot be turned manually becausethe outer gear 42 is held fixed, and the sun gear 28 cannot. be moved bythe planetary gears 38 because of the irreversibility of the wormcoupling to the motor M. However, if the motor M should be rotated, thesun gear 28 is turned, thus turning the member 34 through the planetarygears 38 and driving the shaft 18. This motion is transmitted throughthe sprocket 20 and the chain 22 to the steering wheel shaft 14.

For manual operation, the knob 56 is pulled upwardly, allowing a pin inthe lever 58 to enter a slot in a lever 62 secured to a rotatable shaft64. In the first part of this motion the eccentric 56 rotates the member44 to disengage the gear 42. After the pin 60 engages the lever 62 theshaft 64 is rotated through a predetermined angle. The shaft 64 ispermanently coupled to therotating contacts of a two-position rotaryswitch 66. This switch is provided with conventional stop means fixingthe upper limit of movement of the knob 56, and also detent means tohold the knob in either the upper or lower position.

With the gear 42 freed from the stop member as, the steering wheel maybe turned because, although the sun gear 28 is held fixed as long as themotor M is not turning, the planetary gears 38 are free to revolve aboutthe sun gear. As hereinafter described under the heading CircuitDiagram, the switch 66 deactivates the electrical circuit of the pilot;hence, the motor M is not supplied d with current while the mechanism isin position for manual steering.

As hereinafter more fully explained, the automatic pilot is providedwith certain controls which function according to the rudder position.These controls are associated with the shaft 18 which, as previouslyindicated, is always permanently connected with the steering shaft 14. Aworm 68 fixed to the shaft 18 is engaged with a. worm gear 70 on a shaft72. A pair of cams 74 and 76 are secured to the shaft 72, each cam beingadapted to operate a limit switch 78 or 80 (see also Fig. 6). A pointer82 is secured to the shaft 72 and when the rudder is cen tered thepointer is opposite a fixed arrow 84, preferably inscribed on the frame46. The cams 74 and 76 are respectively adjusted to actuate theirassociated switches when the rudder is turned through a predeterminedangle. In a system actually reduced to practice this angle was 30degrees from center in either direction, as an example. The function ofthe limit switches 78 and 80 is further described in conjunction withFig. 6 under the heading Circuit Diagram.

Also secured to the shaft 72 is a brush 86 of a rudder follow-uppotentiometer 88. Thus the position of the brush 86 bears apredetermined relation to the rudder angle.

A circular plastic or phenolic resin disk 80 having a circumferentialedgewise groove has an eccentric transverse hole to receive the shaft18. The disk is also divided along a chord 92, and the two sections ofthe disk and the shaft are held assembled by a resilient circularmetallic lock spring 94 in the groove. A pair of rivets 96 secure amovable contact member 98 to the disk 90. Thus the member 98 is movablethrough a friction drive from the shaft 18 between a pair of fixedcontacts 100 and 102. The electrical circuit associated with thesecontacts is more fully described in conjunction with Fig. 6, and has asits purpose the stopping ofthe armature of the motor M immediately aftercurrent is removed therefrom by operation of the relays. This assists inpreventing overshooting of the rudder beyond correct steering positionupon the removal of a steering signal.

Binnacle assembly The binnacle assembly is shown in Figs. 2 through 5and consists of the compass and its housing. The compass is supportedwithin a spherical chamber 103 formed by a hemispherical dome 104 ofclear plastic or glass and an inner bowl 106 of phenolic resin or othersuitable material having a similar hemispherical inner wall. Betweenthese two parts is a sealing gasket 107. An annular top ring 108 isfitted over the dome 104 and is provided on its under surface with adepending flange or skirt adapted to fit about an annular shoulderformed by rabbeting the inner bowl 106. The ring 108, the dome 104 andthe bowl 106 are secured together by a number of screws 110 uniformlyspaced about the spherical chamber. Also secured to this assembly is adished and outwardly flanged outer bowl 112, preferably of. the samematerial as the bowl 106, the bowl 112 having an inner annular shoulder114. The bowl 106 has holes 116 by which the space 103 communicates witha space 118, and the bowl 106 also supports an upwardly extending lengthof wire 117 to serve as the lubbers line. The space 118 is sealed by aflexible circular plastic diaphragm 120 having gaskets 122 resting uponthe shoulder 114. The function of the expansible space 113 is toaccommodate thermal expansion of fluid within the spherical chamber 103.This chamber is entirely filled with oil or some other fluid for dampingthe compass card, having a finite but limited viscosity over a widerange of ambient temperatures. The fluid is introduced to the chamberthrough a suitable threaded hole in the inner bowl, filled by a plugscrew, not shown. When this fluid expands, the diaphragm 120 deflectsdownwardly to increase the volume of the space 118.

The foregoing assembly is pivotally supported at its lower end on apivot 124 resting on a pivot plate 125, the pivot being secured by a nut126. Also secured by the nut are a metallic spacer 127 and a contactplate 128 having four slip rings 129. Fixed brushes 130 resilientlybearing upon the slip rings are screwed to a plate 132 mounted on posts134, the posts 134 being secured in turn to a base plate 136 screwed orotherwise firmly secured to the deck.

A generally cylindrical cover 138 is secured by screws 140 to anupwardly turned flange of the base plate 136, thus forming a light-tighthousing about the chamber 103. In'its top face the cover 138 has acentral hole in which is received a stud shaft 140 pivotally supportingthe compass assembly at its upper end. The shaft 140 is secured to agear 142. The gear is secured to a spider 144 having its legs secured byscrews 146 to the ring 108. A pinion 148 is engaged with the gear 142,the pinion being rotatably supported in a hole in the cover 138 andprovided with a knob 150 for changing the course. A disk 152 bearing acompass rose is secured to the shaft 140 and a hub 154 immediately abovethe cover. A post 156 is secured to the cover adjacent the rose forindicating the setting. Also secured to the gear 142 are a pair ofbrackets 158, each supporting an incandescent lamp 160 or 162 adjacentthe dome 104. l

A post 163 is vertically supported within the chambe 103 so as to extendradially upward to support a compass card 164 approximately in adiametral plane. The card 164 is secured 'to a hub 165 which is in turnpivoted about the post 163 by any suitable means allowing sufiicientfreedom of deviation of the card from a perpendicular relationship tothe post as the boat pitches and rolls. Suitablemeans, preferablyincluding a jewel bearing in the tip of the post, are well known in theart and form no part of the present invention. Hence, they are notdescribed in further detail here. The hub 165 also supports one or moreslugs 166 of permanently magnetized material to impart pole-seekingproperties to the rotatable compass card.

In order that the compass may generate electrical signals for coursecorrection upon departure of the vessel from a predetermined heading,the card 164 has a semicircular slot 168 having a diameter approximatelyequal to the distance between the lamps 160 and 162. A pair ofphotosensitive devices 170 and 172are supported adjacent the inner wallof the chamber 103 in positions to receive the light from the lamps 160and 162 when the slot 168 on the compass card is rotated in linetherewith. These photosensitive devices are of any suitable known type,but are preferably variable impedance devices of the type that havesubstantial impedance in total darkness and decreasing impedance as afunction of light impinging thereon. In a tested system considerablesuccess was achieved with glass plates having grids of conductive metal(e.g. gold) embossed thereon, and

also having a coating consisting of a dispersion of cad- I mium sulphideparticles. This construction is well known to the art and has been usedin photographic exposure meters. The devices .174) and 172 are connectedwith isolating resistors 174 and 176, and three connection wires arebrought out through the wall of the chamber 103 for connection tothreeof the slip rings on the plate 128. The fourth slip ring isconnected with one of the common leads from the lamps 160 and and 162(see Figs. 3 and 6), the other lead from the lamps being soldered to thespacer 127 which, through the pivot 124, contacts the fixed metallicpivot plate 125. To insure a good electrical connection the spacer 12?is preferably soldered to the pivot 124.

It will be seen from the above that the binnacle assembly consistsessentially of a compass card pivotally supported within a sphericalchamber 1&3 filled with a damping fluid, the chamber forming a part ofan adjustably pivoted-assembly in a light-tight compartment, and

being provided with photoelectric detecting means in cluding a pair ofphotosensitive devices 170 and 172, and incandescent lamps 160 and 162.When the boat is on course, the lamps 160 and 162 are situated withrespect to the slot 168 in the compass card 164 substantially asillustrated in Fig. 4, whereby an equal amount of light reaches each ofthe devices170 and 172. In that case the magnetic bearing of the boat isindicated by the position of the pointer 156 in relation to the compassrose on the disk 152. A departure of the boat to one side of thisheading results in one of the photosensitive devices 170 or 172receiving more light than the other, and the relationship is reversedfor a departure in the other direction. Connections are made from thelamps and photosensitive devices via the brushes 130 and the bearingplate 125 in the base of the binnacle unit to the circuit shown in Fig.6 which controls the steering motorM (Fig. 1).

Circuit diagram The operation of :the mechanism of-Fig. 1 is controlledby the circuit of Fig. 6 which included the photosensitive elements 170and 172 of the compass unit. It will be understood that the variouscircuit elements of Fig. '6 are illustrated in the relative positionsbest showing the mode of operation. In actuality, a preferredinstallation embodying the invention is divided into four units orchassis interconnected by cables, the binnacle unit '(Figs. 2 to 5)which houses the compass and photosensitive elements, a motor gear boxwhich houses the mechanism of Fig. 1, a remote maneuvering device RMoutlined with broken lines in Fig. 6, and the amplifier-relay chassiswhich houses the balance of the circuit shown in Fig. 6.

As previously stated, the steeering wheel shaft 14 (Fig.

1) is secured to a drive sprocket 16 which is turned by a chain 22during automatic operation. Power is delivered to the chain from asecond sprocket Zilwhichis secured to a shaft 13.. The reversible drivemotor M has a worm gear 30 mounted upon its armature shaft andpermanently coupled to a gear 26, the gear 26 being coupled through theplanetary gear assembly with the shaft 18. For automatic operation thestopmember 44 is rotated into engagement with the external teeth of thegear 42.

Power to drive the motor M is supplied by abattery SB (Fig. 6), which ispreferably the ships battery. The motor has two field coils, a coil FRwhich causes the motor M to turn the rudder to steer right, and a coilFL which causes the motor to turn the rudder to steer left. Currentflows through the coils PR and FL in the directions indicated by thearrows. The coils are selectively connected in series with the armatureof the motor M by closure of the contacts of power relays PR and PL. Thecontacts of the relays "PR and PL are protected against arcing bysuitable condensers 212 and 214. The field circuits also include limitswitches 78 and 88 (Fig. 1), each of which is normally closed duringoperation of the pilot but opened if the rudder angle exceeds apredetermined limit. In the previously mentioned system reduced topractice these switches opened respectively at rudder angles of 30degrees on each side of center. Thus for a change of course requiring arelatively large rudder angle, the rudder reaches and maintains amaximum deflection of 30 degrees until a smaller angle is required asthe new course becomesestahlished.

The motor circuit is also provided with a damping capacitor C controlledby the switch S2. This switch is shown in Fig. 1 and includes the fixedcontacts 100 and through the coil FL in the direction indicated by thearrow, thus opposing the magnetic field in the coil PR and preventingoverrunning of the armature of the motor and the rudder. When the shaft18 rotates in the direction opposite to that just indicated, thecontacts 98 and 102 are closed and opening of the contacts on the relayPL causes the capacitor to discharge through the coil FR, opposing thefield of the coil FL with the same result.

The operation of the balance of the circuit in Fig. 6 is for the purposeof energizing either the relay PR or the relay PL when the vessel is offcourse, and for causing such relay to remain energized a sufficientlength of time to rotate the rudder through the appropriate angle. Thecoils of the relays PR and PL have the positive side of the ship'sbattery SB as a common connection. The relay PR is energized bygrounding a lead 216 and the relay PL by grounding a lead 218. If thesetwo leads should become energized simultaneously for any reason, onlythe relay PR is energized. This bias in favor of the relay PR isproduced by an interlock relay IR having a break contact in series withthe connection between the lead 218 and the relay PL. While simultaneousenergization of the leads 216 and 218 is not a normal condition in thecircuit, it may be brought about by inadvertent operation of the remotemaneuvering device, as for example by simultaneously depressing pushbuttons S and S6 of the remote maneuvering device, hereinafter morefully described. a

The following description explains how the leads 216 and 218 areselectively grounded to steer the boat. Ships battery SB is connected bya lead 220 and a resistor 222 with the incandescent lamps 160 and 162mounted in the binnacle unit adjacent the upper side of the compass card164. This connection is made through a slip ring such as 129 (Fig. 3)and a brush 130, with the return connection being made through the pivot124. The circuit is closed through contacts 228 of the switch 66, whichare closed 'during automatic operation when the master control handle 56is pushed down as shown in Fig. 1.

If the boat is hearing precisely on course, the photosensitive devices170 and 172 receive equal amounts of light. Resistors 230 and 232 areequal, and hence a connection 234 reaches a potential equally dividingthat between leads 236 and 238, the latter leads being connected toopposite terminals of equal B batteries B1 and B2, grounded at theirmutual connection. fore the connection 234 is then substantially atground potential.

The photosensitive devices 170 and 172 form a bridge network with therudder follow-up potentiometer 88 and a manually-operated centeringpotentiometer 240. The bridge network is connected to the emitter-basecircuit of a suitable transistor T of conventional form. The outputcircuit includes a wire 241 connected with the movable contact of apotentiometer 242. The respective functions of the potentiometers 88,240 and 242 are hereinafter further described. For the assumed case of aboat bearing precisely on course, the adjustments are such that thepotential of the base with respect to the grounded emitter produces apredetermined collector current. The

collector circuit includes a pair of coils SR and SL in series, and iscompleted to the battery B2 through normally-closed break contacts of aswitch S3 in the remote maneuvering device RM and break contacts 244 ofthe switch 66. By way of illustration, this current in the previouslymentioned system reduced to practice was 5.1 milliamperes (ma).

If the bearing of the boat becomes off course to the left, thephotosensitive device 170 receives more light from the lamp 160 (seeFig. 4) and hence becomes more conductive, while the photosensitivedevice 172 receives less light from its lamp 162 and becomes lessconductive. This causes the potential at the connection 234 to becomemore positive, relative to the grounded midpoint between batteries B1and B2, and a portion of this positive change Thereis reflected in thepotential at the lead 241. This causes an increase in the collectorcurrent passing through the coils SR and SL. Conversely, if the boatbecomes off course to the right, the photosensitive device 172 becomesmore conductive, thus decreasing the potential at the connection 234 andcausing a decrease in the collector current in the transistor.

The coils SR and SL are referred to as the steering coils, the coil SRforming one winding of a relay RR and the coil SL similarly forming awinding of a relay RL. Each of these relays has a transfer blade 245 or246 and a bias coil BR or BL. In each relay the blade is urged by atension spring 247 or 248 in a direction to increase the air gap in themagnetic path. It will be understood that each relay is of the typehaving two coils, in which the connections thereto are additive oraiding in their effect on the magnetic flux attracting the blade. Inactuality, the structure of the relays may take any one of several formswell known to the art, and are shown in the drawing simply by aconventional symbol. Such forms usually include a pivoted armature forcompleting a portion of the magnetic path and engaging with the blade.These details of structure will be readily appreciated by one skilled inthe art and are not further described herein. 4

It should also be noted with reference to the relays RR and RL, thatwhile a magnetic field of a'certain intensity is necessary in each caseto attract the blade, a lower magnetic field is suflicient to maintainit in the attracted position. In addition, the relay RL is moresensitive than the relay RR, and its blade is attracted by a lessintense magnetic field than that which is necessary to attract the bladeof the relay RR. Thus when the boat is on course, the predeterminedcurrent carried by the steering coils SR and SL is not enough to attractthe blade 245 even though the bias coil BR is also energized. However,this current in the steering coil SL is enough to attract the blade 246with the bias coil BL being also energized. It is apparent that underthis condition neither of the wires 216 nor 218 is grounded and neitherof the power relays PR-nor PL is energized. I

In the drawing the blade 245 is shown in the unattracted position, whilethe blade 246 is shown attracted, this being the condition of thecircuit when the automatic pilot is in operation with the boat oncourse. The blades are connected in common and grounded throughnow-closed break contacts 250 of the switch S3 on the remote controlunit and the now-closed contacts 228 of the switch 66. Thus the outputlead 218 is grounded when the blade 246 is unattracted, while the outputlead 216 is grounded when the blade 245 is attracted. In either case,when the output lead 216 or 218 is not grounded, ground is suppliedthrough the blade 245 or 246 to the bias coil BR or BL, as the case maybe. The current in the bias coils is necessarily constant, since oneside of each of these coils is directly connected with the lead 236, andthe other side of each coil is either open or grounded depending uponthe position of the blade 245 or 246. In the system previouslymentioned, this current was 0.8 ma., for example.

We may now consider the operation of the unit in response to departuresof the boat from the compass setting. For this purpose it is convenientto discuss the operation in terms of the value of collector current inthe transistor T since, as has been previously stated, this current hasa predetermined magnitude, 5.1 ma. in the example, for an on-courseheading, and varies above or below this value depending in part upon theextent and direction of departure from the compass setting. It will beshown at a later point, however, that the collector current is notsolely a function of the departure measured by the compass through thephotosensitive devices and 172, but also of the rudder angle, since thefeedback potentiometer 88 is operated by the rudder steering train.Therefore, the collector current in the 9 transistor is in reality afunction of two variables; the bearing departure of the vessel and therudder angle relative to the vessel.

The above-described condition of the circuit continues, using the givenexample for illustration, as the collector current is increased from5.]. to 5.7 milliamperes, representing a finite but small departure tothe left of course, ordinarily less than one degree in magnitude. Whenthe current reaches 5.7 ma. the magnetic field of the relay RR becomessufiiciently intense to attract the blade 245, thereby causing theoutput lead 216 to be grounded. It will be observed that this alsoremoves current from the bias coil BR, but since this does not occuruntil after the blade has been attracted, the loss of magneticattraction afforded by this current is not sufliciently great to causethe blade to return to its unattracted position.

This condition of the circuit persists for any value of collectorcurrent above 5.7 ma., whereby the motor M causes a continuouslyincreasing deflection of the rudder steering the boat to the right aslong as the blade 245 remains attracted. Under normal conditions thebearing approaches the course setting so that the collector currenteventually is reduced below 5.7 ma. However, the blade 245 remainsattracted until the collector current is reduced to 5.4 ma. for thereason pre viously indicated. When the blade 245 is released the circuitto the motor M is opened and the controls are in the on-coursecondition. The motor M is quickly stopped by the discharge of thecondenser C through the winding FL in the direction indicated by thearrow in Fig. 6, as explained above.

If the boat departs to the right of course, the photosensitive device172 receives increasing light and hence becomes more conductive, whilecell 170 receives less light and its impedance increases. This makes thepotential of the connection 234 more negative, thereby decreasing thecollector current in the transistor T. When this current is reduced to avalue of 4.5 ma. the field of the relay RL is no longer sufficientlystrong to hold the blade 246 attracted even though the bias coil BL iscarrying a current of 0.8 ma. The blade 246 therefore falls back,causing the output connection 218 to be grounded. If the collectorcurrent should decrease to any value below 4.5 ma. this condition of thecircuit persists.

As the boat moves toward the on-course heading, the collector currentincreases, but is not sufliciently strong to attract the blade 246 untilit reaches a value of 4.8 At that current value the blade 246 isattracted, and the circuit is brought back to the on-course condition.

In the system reduced to practice and described above for illustration,the circuit parameters were so selected and adjusted that a range ofdepartures from true course subtending approximately one degree ispermitted before the motor is energized to apply a rudder correction. Innormal operation departures within this range tend to average out,although in case a closer control is desired, the range may be decreasedto any desired fraction of a degree by adjusting the relays RR and R1.to attract their armatures at collector currents more closely equal tothe on-course value. In that case the relay RR would be made moresensitive and the relay RL less sensitive. However, an appreciable deadangle, so-called, is preferable in order to reduce the: tendency of thecircuit to hunt" and thus cause substantially continuous operation ofthe steering motor.

As previously stated, the voltage applied to the emitter-base circuit ofthe transistor T is a function of the error signal from thephotosensitive devices 170 and 172, and also of the positions of thepotentiometers 240, 88 and 242.

One of the conditions governing the potentiometer settings is that whichpertains to the on-course heading. For this heading the connection 234is substantially at ground potential. The common potential at themovable contacts of the potentiometers 240 and 88 is positive. A portionof this positive voltage appears at the movable contact of thepotentiometer 242 and at the base of the transistor. This gives rise toa predetermined collector current, which in the tested system was 5.1ma.

A departure to the left of course gives rise to a positive increase inthe potential of the connection 234, and hence to a correspondingpositive increase in the voltage applied to the transistor. Conversely,a departure to the right causes the potential of the connection 234 tobecome more negative, and hence to cause a like change in the voltageapplied to the transistor.

As the motor M rotates the rudder in response to a bearing departuresignal, the movable contact of the potentiometer 88 is correspondinglymoved. This movement is to the left as viewed in Fig. 6 when the ruddersteers to the left, and to the right when the rudder steers to theright. Thus if the boat departs to the left of course, tending to causean increase in the transistor current, the change in the potentiometer88 resulting from the responsive movement of the rudder tends todecrease the transistor current to some extent.

As a result, the circuit applies a relatively large potential to thetransistor for a given bearing deviation if the rudder is centered, anda decreasing potential for the same bearing departure resulting from theappropriate responsive deflection of the rudder. In other words, thecircuit is progressively desensitized with an increasing rudderdeflection, thus tending to prevent the application of excessive rudderdeflections and to produce a smooth steering movement of the boat, whichis particularly noticeable when the helmsman introduces a radical changein course at the binnacle unit.

The same considerations apply when the movable contact of thepotentiometer 88 moves to the left as viewed in Fig. 6, corresponding toa bearing departure to the right of course and a responsive movement ofthe rudder to steer toward the left. 'In this case an increasing rudderdeflection tends to counteract in part the eifect of the negativepotential at the connection 234.

The potentiometer 240 is connected in the same way as the potentiometer88 and is provided with a manual adjustment knob. By this means it ispossible to set the potentiometer 88 at a given position for a zerorudder deflection, and then to make adjustments in the potentiometer 240until the emitter-base current in the transistor is at the desired valuefor the on-course head- :ing. The manually adjusted potentiometer 242 isused as a ratio control, and from the foregoing discussion it will beapparent that its function is to determine the sensitivity of thetransistor to the. bearing departure signal at the connection-234. Thusupward movement of the contact on the potentiometer 242, as viewed inFig. 6, decreases the sensitivity of the circuit to bearing departures,and downward movement increases the sensitivity. I

The circuit is also preferably adjusted so that variations in the signalapplied to the transistor are produced only for hearing departureswithin a predetermined :angle less than the limit value set by theswitches 78 and 80 on either side of center. In the system reduced topractice and discussed above, this angle was 18 degrees, whereby abearing departure of more than that angle in either direction producedsubstantially the same error signal at the connection 234 as adeflection equal to that angle. This feature tends to limit the responseof the device to the normal range of steering operation, and to resultin smoothness of steering.

Remote maneuvering device During operation of the automatic pilot, itmay occasionally be necessary to take over manual control for a shorttime'to perform adodging maneuver or for some other reason.

11 One method of doing thisis to pull up the master control knob 56,whereby the switch 66 is opened and the circuit is put out of action andsecured. The rudder may then be turned by the steering wheel 12.

According to this invention, another alternative control is provided,which consists of a portable remote maneuvering control box RMcontaining the switches S3, S and S6, this box being connected with thepilot circuit through a six-Wire cable of substantial length, enablingthe vessel to be maneuvered from any desired point remote from thesteering wheel.

The switch S3 is a toggle switch having two stable positions, theposition shown in Fig. 6 corresponding to automatic operation aspreviously described, and the opposite position corresponding tooperation from the remote maneuvering device. The switches S5 and S6 areof the push-button type, and are closed only while held depressed. i

When the switch S3 is operated for remote maneuvering, ground is removedfrom the steering coil circuit by opening of contacts 252 and neither ofthe blades 245 or 246 is attracted. The ground connection to the bladesis also removed by the contacts 250. For steering to the right theswitch S5 is depressed, thereby energizing the relay PR by grounding thelead 216 through make contacts of the switch S3. For steering to theleft the switch S6 is depressed, thereby grounding the lead 218. As inthe case of automatic operation, the limit switches 78 and 80 preventthe rudder from reaching an angle of more than a predetermined value oneither side of center. To return to automatic operation the switch S3 ismerely returned to its original position. n

From the foregoing description of the structure and operation of theinvention, it will be appreciated that, although all of the essentialproperties of a convertible automatic and remote pushbutton pilot deviceare provided, considerable simplification has been achieved. As aresult, it becomes feasible to employ the invention in smaller craftwhere space for installation is likely to be limited. In use as anautomatic pilot, immediate accurate response automatically and smoothlyfollows upon each new course setting of the binnacle unit. The helmsmanis merely required to rotate the knob 150 until the desired heading onthe compass rose is opposite the fixed pointer 156. The boatautomatically maintains the desired heading, allowing only a smallbearing departure before application of corrective rudder. When at thewheel, the helmsman may take over positive manual control simply bypulling up the master control knob 56. At any time while the pilot is onautomatic operation, it may be disengaged simply by moving the toggleswitch S3 on the remote maneuvering device RM, after which steering maybe accomplished remotely by means of the two pushbuttons S5 and S6.Automatic operation is resumed simply by moving the switch S3 back toits original position, after which the course setting on the binnacleunit becomes immediately effective.

It will be understood that the foregoing description of a preferredembodiment of the invention has been given solely for the purpose offacilitating a clear understanding thereof, and that such modificationsin design, structure or arrangements of the parts as would occur to oneskilled in the art upon a reading of the description are within thespirit and scope of the invention.

Having thus described the invention, I claim:

1. A pilot control having, in combination, a transistor, a pair ofrelays having coils connected in series with the emitter-collectorcircuit of the transistor, a voltage source in series with said coils insaid circuit, said relays having differing sensitivities, a compasshaving setting means, a pair of photosensitive elements in theemitter-base circuit of the transistor, a light source, a compass cardadapted to modulate the emitter-base current through modulation 12 ofthe light from said source reaching said elements as a function of thedeparture from the set course,- said emitter-base current causingattraction of the armature of only one of said relays when the headingis on course, and steering means responsive to the armature positions ofsaid relays. 4

2. A pilot control having, in combination, a device having at leastthree terminals and an impedance between two of the terminals varyingwith the voltage applied between one of said terminals and the thirdterminal, a pair of relays and a voltage source connected in series withsaid variable impedance, said relays having differing sensitivities, acompass having setting means and means adapted to vary said firstrecited voltage according to the departure from the set course, thecurrent in said relays causing attraction of the armature of only one ofsaid relays when the heading'is on course, and steering means responsiveto the armature positions of said relays.

3. A pilot control having, in combination, a device having at leastthree terminals and an impedance between two of the terminals varyingwith the voltage applied between one of said terminals and the thirdterminal, a pair of relays and a voltage source connected in series withsaid variable impedance, said relays having differing sensitivities, acompass having setting means, a pair of photosensitive elements, a lightsource, a compass card adapted to modulate the light from said sourcereaching said elements as a function of the departure from the setcourse, a bridge network including said photosensitive elements to varysaid first recited voltage in a corresponding manner, the current insaid relays causing attraction of the armature of only one of saidrelays when the heading is on course and causing attraction ornon-attraction respectively of both said armatures when the heading isoff course in one or the other direction, and steering means responsiveto the armature positions of said relays. I

4. A pilot control having, in combination, a device having at leastthree terminals and an impedance between two of the terminals varyingwith the voltage applied between one of said terminals and the thirdterminal, a pair of relays and a voltage source connected in series withsaid variable impedance, said relays having differing sensitivities,steering means responsive to the armature positions of said relays, anda compass having setting means, means adapted to produce a variablevoltage according to the departure from the set course, a

ratio-control impedance adapted to apply a variable portion of saidlast-mentioned voltage to said device to vary its said impedance, thecurrent in said relays causing attraction of the armature of only one ofsaid relays when the heading is on course.

5. A pilot control having, in combination, a device having at leastthree terminals and an impedance between two of the terminals varyingwith the voltage applied between one of said terminals and the thirdterminal, a pair' of relays each having two windings connected in aidingrelationship, one winding of each relay being in series with saidvariable impedance, a voltage source in series with said variableimpedance, contacts for the relays to energize the other winding of eachrelay in only one position of its armature, said relays having dilferingsensitivities, a course heading reference, means adapted to vary saidvoltage according to the departure from the set course, the current insaid windings causing attraction of the armature of only one of saidrelays when the heading is on course, and steering means responsive tothe armature positions of said relays.

6. A pilot control having, in combination, a device having at leastthree terminals and an impedance between two of the terminals varyingwith the voltage applied between one of said terminals and the thirdterminal, a pair of relays and a voltage source connected in series withsaid variable impedance, said relays having difiering sensitivities,reversible steering means, a compass having setting means and meansadapted to vary said first recited voltage according to the departurefrom the set course, the current in said relays causing attraction ofthe armature of only one of said relays when the heading is on course,circuit means to power said steering means through the contacts of saidrelays, and a remote maneuvering device including switches for closingsaid circuit means independently of said relays.

7. A pilot control having, in combination, a device having at leastthree terminals and an impedance between two of the terminals varyingwith the voltage applied between one of said terminals and the thirdterminal, a first pair of relays and a voltage source connected inseries with said variable impedance, said first pair of relays havingdiffering sensitivities, reversible steering means, a course headingreference, and means adapted to vary said voltage according to thedeparture from the set course, the current in said first pair of relayscausing attraction of the armature of only one of said relays when theheading is on course, a second pair of relays adapted to power saidsteering means through the contacts of said relays, the contacts of saidsecond pair of relays being adapted to remain open in the on-coursecondition of said first pair, and a remote maneuvering device includingswitches for opening said series circuit and closing said second pair ofrelays independently of said first pair of relays.

8. The apparatus of claim 7 wherein said steering means comprise incombination, a steering shaft, a motor engaged with the shaft, the motorhaving a pair of field coils and an armature each having a connection incommon, a source of electrical energy, means to complete a circuit fromthe source through the armature and one of said field coils in series, acondenser, and a frictiondriven transfer switch on said shaft to connectthe condenser across the armature and the unenergized field coil inseries while said circuit is completed, whereby when said circuit isopened the condenser discharges through the last-mentioned coil in theappropriate direction to exert a braking force on said armature.

References Cited in the file of this patent UNITED STATES PATENTS1,662,133 Smith Mar. 13, 1928 2,228,078 Gulliksen I an. 7, 19412,306,784 Lord Dec. 29, 1942 2,340,175 Chance Ian. 25, 1944 2,342,105Jacobi Feb. 22, 1944 2,387,795 Isserstedt Oct. 30, 1945 2,446,299 NelsenAug. 3, 1948 2,468,653 Bridges Apr. 26, 1949 2,472,566 Brown et al. June7, 1949 2,498,223 Rommel Feb. 21, 1950 2,579,336 Rack Dec. 18, 19512,609,513 Boucher et al Sept. 2, 1952 2,777,070 Stamper et a1 Jan. 8,1957 FOREIGN PATENTS 728,615 Germany Nov. 30, 1942 OTHER REFERENCESPublication, Using a Transistor to Increase Relay Sensitivity, Radio andTelevision News, June 1953, page 39.

